1. Field of the Invention
The present invention relates to a laser beam recorder for recording an image on a record medium by using a laser beam.
2. Description of the Prior Art
FIG. 1 shows a basic configuration of a laser beam printer, in which numeral 1 denotes a photosensitive (or photoconductive) drum, numeral 2 denotes a laser oscillator for generating a laser beam, numeral 3 denotes a collimator lens, numeral 4 denotes a scanner (polygon) for deflecting the laser beam, which is rotated in a direction of an arrow, numeral 5 denotes a focusing lens and numeral 6 denotes a controller for controlling the scanner.
In the laser beam printer, a pre-rotation process of the photosensitive drum is started in response to a start of print signal, and after the pre-rotation, the laser beam emitted by the laser oscillator 2 is modulated by a video signal, the modulated laser beam is converted to a narrow collimate beam by the collimator lens 3, the collimated beam is reflected by the polygon mirror of the scanner 4 which rotates at a predetermined speed, and the reflected beam is directed to the photosensitive plane of the rotating photosensitive drum 1 through the focusing lens 5 to form a latent image on the photosensitive drum 1. The polygon mirror of the scanner 4 is rotated by a scanner motor to scan the laser beam in a direction of an arrow (horizontally) on the photosensitive drum 1. In order to stably rotate the polygon mirror to orderly irradiate the laser beam to the photosensitive drum 1, the rotation speed of the scanner motor is precisely controlled by the controller 6.
However, in the prior art laser beam printer of this type, as shown in a flow chart of FIG. 2, when power is turned on (step S1), the scanner 4 starts to rotate independently from the rotation of the photosensitive drum 1 (step S2), maintains the rotation after a predetermined rotation speed has been reached (step S3), and the rotation of the scanner 4 is stopped (step S5) after the power is turned off (step S4). Accordingly, the scanner 4 continues to rotate while the power is supplied, and hence the lifetime of the scanner 4 is relatively short. The lifetime of the scanner 4 is directly reflected to the lifetime of the laser beam printer.
In the prior art laser beam printer, if the predetermined rotation speed of the scanner 4 is not reached at the end of the pre-rotation period, a printer error condition due to misrotation of the scanner may take place.